Shot-noise transducers



A ril 12, 1960 R. LAMBERT 2,932,801

SHOT-NOISE TRANSDUCERS Original Filed July 26, 1952 2 Sheets-Sheet 2 TUBE NOISE SUPPRESSORS T;- 480 467 FIG.

TUBE NOISE SUPPRESSORS INVENTOR.

RAY LAMB ERT MS Imam/7 SHUT-NOISE TRANSDUCERS Ray Lambert, Cincinnati, Ohio Original application July 26, 1952, Serial N 301,055,

now Patent No. 2,791,686, dated May 7, 1957. Divided and this application November 19, 1956, Serial No. 626,794

7 Claims. (Cl. 330-149) The specification and drawings describing this invention were included in application Serial 301,055 and in Patent No. 2,791,686.

My invention relates to radio noise control and more particularly pertains to the elimination of certain electrical impulses causing noise and originating in the receiver circuit due to thermionic and electronic irregularities in tube and other circuit elements.

These noise impulses are encountered not only in the common broadcast band but in bands above and below, including high frequency and television service. Examples are tube noises and thermal noises in resistors. The problem is to eliminate the effects of these electrical impulses originating in the receiver circuit itself.

Noise effects may be caused by the impulse excitation of tuned circuits and other circuits capable of oscillating under electrical shock or impulse. Very sudden or in stantaneous impulses produce equal voltage amplitudes in all simple tuned circuits. The response differs in the duration of the ensuing wave train in the tuned circuit as a function of the circuit Q or decrement and as a function of the natural frequency of the tuned circuit. The effects of noise impulses having a longer time of voltage rise (lower dE/dz) differ between circuits of different frequency having, in general, a greater elfect the lower the frequency of the tuned circuit.

The form of the response in terms of the voltages developed in a tuned circuit by a sharp or instantaneous impulse is expressed by the formula,

and the response of a tuned circuit under the impact of a voltage variation the duration of which is much greater than the period of the tuned circuit is given by the relation,

+e-" cos (wt-mos {1 4L w In the above expressions V is the voltage of the impulse having a time constant RC, and r, L, and w represent resistance, inductance and angular velocity in the tuned circuit.

The noise effects discussed above may be studied and measured without the presence of a radio frequency signal in the system. A greater cause of noise in radio reception is the modulation of the carrier in the radio frequency amplifier and frequency conversion tubes by the noise impulses. This is due simply to the fact that in most cases these tubes offer different transconductance values with different grid potentials. Hence, a tube noise impulse in changing momentarily the grid voltage changes momentarily the amplification of the signal, causing modulation. After the carrier is modulated in such a manner the noise cannot be removed subsequently in the radio receiver circuit. At this point the noise impulses beatom come a part of the audio signal and cannot be removed any more than an element of speech or music.

The operation of the radio frequency tubes on the straight portion of the grid-voltage plate-current curve is essential for the purpose of noise suppression.

The principal object of my invention is to provide for the cancellation of tube and circuit noises. In this system, circuit noises such as the thermal noise in grid resistors, are not treated separately but only in conjunction with tube noises with which they are associated. Such tube and circuit noises may not be treated as a single unit in the radio receiver because they do not enter the system at any one place or from one causethey are everywhere. These tube noise impulses and certain elements of the thermal noise impulses are thought to be very sharp, approximately instantaneous impulses. These cause impulse excitation of a tuned circuit in the plate of the tube and, to a smaller extent, in a tuned circuit in the grid of the tube. To a still smaller degree the screen grid partition current causes noise by its sudden effect on the value of the plate current.

The basic principle underlying the control of tube and circuit noise excitation of associated tuned circuits as described herein consists in changing the energy of these impulses to a form that may be dissipated without damage to the received signal. In the radio frequency stages the energy of the tube noise impulses may be stored as electrostatic energy and dissipated gradually or stored as magnetic energy and discharged gradually. In the audio stages the energy of these impulses may be converted into energy of a high frequency and dissipated in a harmless manner or may be removed by an appropriate filtering arrangement.

Noises arising from the operation of the amplifier tubes and associated resistances may be reduced thirty decibels or more by the storage of the energy of the noise impulses at or near their sources and by dissipating this energy in a harmless manner. This operation may take the form of capacitive storage with appropriate time constant (RC) or by magnetic storage in radio frequency circuits.

In the schematic drawings:

Figs. 1 and 2 illustrate tube noise suppressors;

Figs. 3, 4 and 5 illustrate methods of suppressing screen-grid partition current noise;

Figs. 6 and 7 are modifications of Fig. 1.

Throughout this description it will be assumed that the amplifier tubes are operated linearly, with grid swing confined to the linear portion of the grid-voltage plate -current (E -J characteristic and that the most positive grid swing does not draw grid current.

The suppression of tube noises in radio frequency circuits may be accomplished by capacity storage of the energy of the tube noise impulses as shown in Fig. 1 or by magnetic storage as shown in Fig. 2. In Fig. 1 condenser 476 and resistance 475 are connected in series in the plate lead of tube 473. The tube noise impulse, impinging on the condenser 476, connected to the plate of tube 473 and plate load resistance 474, causes a current to flow through the resistance 475. Terminal 48d connects to a source of plate voltage, filter not shown. The value of the current through the resistor 475 is determined by the voltage of the impulse and the time constant, RC, of the combination, condenser 476 and resistance 475, with the result that a voltage drop, due to the impressed impulse, is caused in the resistance 475, isolating the effect from the output 477. This current also is found in a reactive or tuned circuit connected across the output terminals 477 and 478, but the voltage 3 drop across this output load, not shown, will be relatively slight if the time constant, RC, of resistance 475 and condenser 476 is 20 or 30 times the period of the output load.

These tube noise suppressors should be designed with reference to the loads out of which and into which they operate, and should be connected as close to the plate terminal of tube 473 as practicable.

A tube noise suppressor consisting of condenser 470 and resistance 471 should also be inserted between the grid of tube 473 at its junction with its grid resistance 472 and its input transformer 468. Noise impulses affecting the grid of tube 473 are relatively slight but they excite the grid tuned circuit 468 to oscillation and this signal is amplified by the tube 473.

Figure 1 represents a generalized radio frequency tuned circuit of which terminals 465 and 466 represent the input to transformer 468 and terminals 477 and 478 represent the output connection to the utilizing device. A ground is provided at 467. Terminal 480 is the connection to the plate voltage supply. 7

The tube noise suppressors consisting of condenser 470 and resistance 471 in the grid circuit of tube 473, Fig. 1, and condenser 476 and resistance 475 in the plate circuit of tube 473 may be reversed, with the condensers placed adjacent to the tube causing only slight changes in operation. See the noise suppressors 470471 and 475-476 in Fig. 6. Other numbers in Fig. 6 correspond to similar numbers in Fig. 1. The grid grounding resistor 472 and the plate resistor 474 may be connected between the condenser and resistance portions of the noise suppressor. See Fig. 7. The numbers in Fig. 7 correspond to similar numbers in Fig. 1. V

Fig. 2 shows the use of choke coils 485 and 491 of a high L/R ratio (time constant characteristic) in place of the condenser-resistance noise suppressors (470-471, 475476 in Figure l). The design of coils 485 and 491 should include low distributed capacity and a natural frequency greatly in excess of the band being received. The high L/R value-is attained by using extremely low values of R. In this case the plate voltage may be fed directly to the plate of tube 486 through the primary of the coupling transformer 492 from the plate voltage supply terminal 495. In Fig. 2, coil 487 has characteristics similar to coils 485 and 491 and is used to reduce the noise effect due to the screen-grid partition current through the process of momentary storage of energy. Resistance 488 and condenser 489 are the'conventional isolating filter in the screen voltage supply.

Other circuit elements in Fig. 2 are conventional. The input terminals 481 and 482 are connected to the primary of the input transformer 484 which is grounded at 483 and the output is indicated at terminals 493 and 494.

Figs. 3, 4 and 5 show a method of controlling the factor of tube noise due to the screen partition current. However, these connections modify greatly the operation of the tube. Its operation with this connection resembles triode operation but is slightly more quiet than the operation afforded by connecting screen and plate directly.

In Figs. 3, 4 and 5 the screen bypass condensers 501, 511, 522 are connected to the plate of tubes 500, 509 and 520 instead of the usual connection to ground. The connection of the screen to the plate through condenser 501, 511 or 522 suppresses only that portion of the tube noise due to the screen partitioncurrent and is not a substitute for the tube noise suppressors shown in Fig. 1. The screen grid voltage supply is then provided by a series resistor 502 in Fig. 3, 512 in Fig. 4 and 523 in Fig. 5. The plate voltage is applied through resistance 503 in Fig. 3, 513 in Fig. 4 and through resistances 523 and 524 in Fig. 5, taken from the plate voltage supply terminals 508, 517 and 528 respectively. Output coupling condensers 504, 514 and 525 connect to output terminals 505, 515 and 526 respectively. Grounds are provided at 507, 510 and 521 in Figs. 3, 4 and 5, connected to the grounded output terminals 506, 516 and 527 respectively.

Other arrangements of voltage feed to the screen and plate of tubes may be employed.

I am aware that the device herein described issusceptible of considerable variation without departing from the spirit of my invention, and therefore, I have claimed my invention broadly as indicated by the appended claims. Having thus described my invention what I claim is new and useful and desire to secure by United States Letters Patent is:

1. In a radio Wave-signal receiver comprising a thermionic vacuum tube and a signal coupling device in the output circuit of said thermionic vacuum tube: a'

tube-noise suppressor, connected between the output terminal of said thermionic vacuum tube and said signal coupling device, said tube-noise suppressor comprising a resistor and capacitor in series, the values of said resistor and capacitor selected to give a time constant significantly greater than the time of a quarter period of the transformer, said combination of resistor and capacitor in series having assigned values of resistance and capacitance designed to give a time constant significantly greater than the time of a quarter period of the wave signal in the aforesaid wave-signal receiver.

3. In a radio wave-signal receiver comprising a thermionic vacuum tube and a signal coupling device in: the output circuit of said thermionic vacuum tube: an inductive element is connected between the output terminal of said thermionic vacuum tube and said signal coupling device in the output circuit of said thermionic vacuum tube, said inductive element consisting of a coil having a natural resonant frequency greatly in excess of the frequency of the wave signal of the aforesaid wavesignal receiver and having an inductance-resistanceratio designed to give a time constant significantly greater than the time of a quarter period of the wave signal in the aforesaid wave-signal receiver.

4. In a radio wave-signal receiver comprising a thermionic vacuum tube, a radio-frequency transformer in the output circuit of said thermionic vacuum tube and a radio-frequency transformer in the input circuit of said thermionic vacuum tube: a combination of a resistor and capacitor in series is inserted between the output terminal of the above said thermionic vacuum tube and the primary of the above said radio-frequency transformer in the output circuit of above said thermionic vacuum tube and a second combination of resistor and capacitor in series is inserted between the input terminal of the above said thermionic vacuum tube and the secondary of the said radio frequency transformer in the input circuit of said thermionic vacuum tube, each aforesaid combination of resistor and capacitor in series consisting of resistive and capacitive values designed to give a time constant significantly greater than the time of one quarter period of the wave signal in the aforesaid wave-signal receiver.

5. In a radio wave-signal receiver comprising a thermionic vacuum tube, a signal coupling device in the output circuit of said thermionic vacuum tube and a reactive signal coupling device in the input circuit of said thermionic vacuum tube: an inductive element connected between the output terminal of the above said thermionic vacuum tube and the above said signal coupling device in the output circuit of said thermionic vacuum tube and a second inductive element connected between the input terminal of the above said thermionic vacuum tube and the above said reactive signal coupling device in the input circuit of said thermionic vacuum tube, each above said inductive element consisting of a coil having a natural resonant frequency greatly exceeding the frequency of the wave signal of the above said wave-signal receiver and each said inductive element having an inductiveresistance ratio designed to give a time constant signifi cantly greater than the time of a quarter period of the wave signal in the aforesaid wave-signal receiver.

6. In a radio wave-signal receiver comprising a thermionic vacuum tube, a resonant coupling device in the output circuit of said thermionic vacuum tube and a resonant coupling device in the input circuit of said thermionic vacuum tube: an inductive element connected between the output terminal of the above said thermionic vacuum tube and the above said resonant coupling device in the output circuit of said thermionic vacuum tube and a second inductive element connected between the input terminal of the above said thermionic vacuum tube and the above said resonant coupling device in the input circuit of the said thermionic vacuum tube, each above said inductive element consisting of a coil having a natural resonant frequency greatly exceeding the frequency of the wave signal of the above said wave-signal receiver and each said inductive element having an inductanceresistance ratio'designed to give a time constant significantly greater than the time of a quarter period of the wave signal in the aforesaid wave-signal receiver.

7. In a radio Wave-signal receiver comprising a thermionic vacuum tube, a signal coupling device in the output circuit of said thermionic vacuum tube and a resonant signal coupling device in the input circuit of said thermionic vacuum tube: two tube-noise suppressors are provided, one of said tube-noise suppressors connected between the output terminal of the above said thermionic vacuum tube and the above said signal coupling device in the output circuit of said thermionic vacuum tube, the other of the above said tube-noise suppressors connected between the input terminal of the said thermionic vacuum tube and the above said resonant signal coupling device in the input circuit of the said thermionic vacuum tube, one of the above said tube-noise suppressors consisting of an inductive element, said inductive element consisting of a coil having a natural resonant frequency greatly exceeding the frequency of the wave signal of the above said wave-signal receiver, said inductive element having an inductance-resistance ratio designed to give a time constant significantly greater than the time of a quarter period of the wave signal in the aforesaid wavesignal receiver and the other of the above said tubenoise suppressors consisting of a capacitor and resistor in series, the capacitance and resistance values of said capacitor and resistor in series designed to give a time constant significantly greater than the time of a quarter period of the wave signal in the aforesaid wave-signal receiver.

References Cited in the file of this patent 

